Several methods have in the past been employed in the laying of submarine pipe in segments, hereinafter referred to simply as sections. These prior systems included employment of various screw jacks, collars attached to the pipe, and the like, connected by divers between the prior laid pipe and the section being laid, the latter sometimes being made more easily maneuverable by attaching buoyancy elements thereto. However, great difficulty has been encountered in preventing dislocation of the prior laid pipe and the system is generally very laborious and slow.
In maneuvering larger, heavier sections, cables or the like have in the past been employed to transmit movement of a surface floating platform, with derricks or the like, to the suspended section and again divers have been used to direct such movement of the surface platform. This system is also slow, hazardous and expensive, again partly due to the tendency for the prior laid pipe to be dislodged, the inherent and underlying difficulty being that the surface floating platform is seldom perfectly stable and control movements of the suspended section is erractic and unpredictable in degree as a result.
Another method was characterized by dependence on a flexible cable connected to the section being laid and extending, axially through the portion of the line of pipe already in place, to a winch, usually installed on shore, to pull the new section longitudinally into place.
Still another method has been employed in the recent past, with questionable efficiency, this system involving use of a fixed platform supported on the offshore bay or ocean floor, lake bed or river bed by extensible legs of great length, the pipe sections being lowered from or through the platform which is moved forward as each section or small number of sections is laid. This system is reasonably successful in laying pipe in shallow water but failed when greater depths of water were encountered.
Numerous variations of the above briefly described methods have been evolved. The difficulties involved in all their prior systems, other than those obviously evident, include the very important factor of rapidly accelerating costs when the depth of the water is increased beyond a few feet and most of the prior systems become infeasible when the depth of the water exceeds one hundred feet.